title: Mutations in palmitoyl-protein thioesterase 1 alter exocytosis and endocytosis at synapses in Drosophila larvae.
abstract: Infantile-onset neuronal ceroid lipofuscinosis (INCL) is a severe pediatric neurodegenerative disorder produced by mutations in the gene encoding palmitoyl-protein thioesterase 1 (Ppt1). This enzyme is responsible for the removal of a palmitate group from its substrate proteins, which may include presynaptic proteins like SNAP-25, cysteine string protein (CSP), dynamin, and synaptotagmin. The fruit fly, Drosophila melanogaster, has been a powerful model system for studying the functions of these proteins and the molecular basis of neurological disorders like the NCLs. Genetic modifier screens and tracer uptake studies in Ppt1 mutant larval garland cells have suggested that Ppt1 plays a role in endocytic trafficking. We have extended this analysis to examine the involvement of Ppt1 in synaptic function at the Drosophila larval neuromuscular junction (NMJ). Mutations in Ppt1 genetically interact with temperature sensitive mutations in the Drosophila dynamin gene shibire, accelerating the paralytic behavior of shibire mutants at 27 °C. Electrophysiological work in NMJs of Ppt1-deficient larvae has revealed an increase in miniature excitatory junctional potentials (EJPs) and a significant depression of evoked EJPs in response to repetitive (10 hz) stimulation. Endocytosis was further examined in Ppt1-mutant larvae using FM1-43 uptake assays, demonstrating a significant decrease in FM1-43 uptake at the mutant NMJs. Finally, Ppt1-deficient and Ppt1 point mutant larvae display defects in locomotion that are consistent with alterations in synaptic function. Taken together, our genetic, cellular, and electrophysiological analyses suggest a direct role for Ppt1 in synaptic vesicle exo- and endocytosis at motor nerve terminals of the Drosophila NMJ.
authors.affiliation: Department of Biology; Pomona College; Claremont, CA USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Aby
authors.affiliation: Department of Biology; The College of Charleston; Charleston, SC USA.
authors.forename: Katherine
authors.initials: K
authors.lastname: Gumps
authors.affiliation: Department of Biology; Pomona College; Claremont, CA USA.
authors.forename: Amalia
authors.initials: A
authors.lastname: Roth
authors.affiliation: Department of Biology; The College of Charleston; Charleston, SC USA.
authors.forename: Stacey
authors.initials: S
authors.lastname: Sigmon
authors.affiliation: Department of Biology; Pomona College; Claremont, CA USA.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Jenkins
authors.affiliation: Department of Biology; Pomona College; Claremont, CA USA.
authors.forename: Joyce J
authors.initials: JJ
authors.lastname: Kim
authors.affiliation: Department of Neuroscience; Pomona College; Claremont, CA USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Kramer
authors.affiliation: Department of Biology; Pomona College; Claremont, CA USA; Program in Molecular Biology ; Pomona College; Claremont, CA USA.
authors.forename: Karen D
authors.initials: KD
authors.lastname: Parfitt
authors.affiliation: Department of Biology; The College of Charleston; Charleston, SC USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Korey
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D004705:Endocytosis / Q000235:genetics*; D005089:Exocytosis / Q000235:genetics*; D007814:Larva / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D008124:Locomotion / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D009154:Mutation; D009469:Neuromuscular Junction / Q000254:growth & development / Q000378:metabolism; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D013869:Thiolester Hydrolases
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D013869:Thiolester Hydrolases; C498814:Ppt1 protein, Drosophila
keywords: Batten disease; Drosophila; endocytosis; exocytosis; infantile neuronal ceroid lipofuscinosis; palmitoyl-protein thioesterase-1; synaptic vesicle cycling